New generation propeller repair equipment used for cropping in Singapore

28/02/2014

Recently a team of Hydrex diver/technicians performed a propeller blade operation on a 300-meter container vessel in Singapore. All six blades of the vessel’s propeller were damaged and needed to be cropped.

Having developed different procedures for different kinds of damage, Hydrex is equipped and trained to make the best of a bent or broken propeller. Ideally, the in-house developed cold straightening technique is used. This procedure enables Hydrex to straighten damaged blades in-water, allowing commercial operations to continue without the need to drydock.

In the following example cropping was the only option as the damage to the propeller blades was too great to allow cold straightening. This kind of repair is carried out with the propeller blade cutting equipment developed by the Hydrex research department. In cases where there is an even number of blades an identical piece will be cropped from the opposite blade to restore the hydrodynamic stability of the propeller. By doing so, the best possible efficiency is obtained.

The six blades of a container vessel’s propeller were severely bent. An on-site solution was needed to restore the propeller’s balance and efficiency. A Hydrex diver/technicians team was therefore rapidly mobilized to the ship’s location to restore the damaged blades to as close to their original condition as possible.

Because the ship could be trimmed enough to bring the blades above water, a scaffolding was installed around the propeller. This allowed the team to perform the operation in the dry.

The operation started with a detailed survey of the affected propeller blades. The inspection revealed that the six blades were bent over angles of up to 90 degrees. The team then used the information acquired during the inspection to calculate and determine the correct measurements needed to modify the trailing edges of the propeller blades. Next the divers cropped the blades one by one to give them the correct radius. When the cropping was complete, the blades were polished to make sure that any remaining loss of efficiency would be minimal.

The success of the operation was confirmed by the customer. After the operation the vessels completed sea trial and “managed to increase RPM up to 93 and developed 21 knots,” said Maxim Bolduev, Deputy Fleet Manager Southern Shipmanagement. “Before propeller trimming we got 53 RPM and only 14 knots.”

Conclusion
Our R&D department is constantly looking into ways to enhance the available propeller repair techniques even further to improve our services. New models of both the straightening and the cutting machines have recently been put into service. These allow us to straighten blades that could previously only have been cropped and to crop extremely damaged blades with only a minimal loss of efficiency for the propeller. Both types of repairs can be carried out on-site and underwater, allowing the ship to return to commercial operations without the need to drydock.